To increase both the output and the efficiency, ever increasing turbine inlet temperatures have been used in modern gas turbine power plants. Unfortunately, these higher temperatures have jeopardized the integrity of the turbine components. In order to protect the turbine components from high temperature, both convective cooling and film cooling can be used.
Turbine vane and blade cooling arts disclose various configurations for enhancing film cooling effectiveness and reducing the required amount of cooling air in order to increase the overall efficiency of the engine while obtaining a suitable useful life for the vanes and blades. For example, typical vane and blade airfoils in the high pressure turbine section of the engine include cooling holes that extend through the pressure side, or suction side, or both, for discharging a film of cooling air along the outer surface of the airfoil to effect film cooling in a conventional manner.
Film cooling effectiveness depends on many factors. One such factor is the length of the hole. Film cooling effectiveness is proportional to the length of the hole. However, reduced wall thickness designed to increase the effectiveness of both convective cooling and film cooling, may present a challenge since it limits the length of hole.